Evaluation of the extent of protein binding by means of NMR diffusion and relaxation experiments, and automated continuous ultrafiltration

The extent of protein binding is one of the key parameters in both pharmacodynamics and pharmacokinetics. Since a high protein binding prevents the drug to reach the target enzyme or receptor in the organism and the metabolism and excretion of drug, a low protein binding is preferable. Thus, the protein binding has to be considered in the process of drug development. In order to keep the extent of protein binding low it is necessary to know the mechanism of protein–drug interaction. Because NMR methods are able to provide such structural information the purpose of this paper is to compare relaxation and diffusion NMR experiments with a classical protein binding determination method, i.e. ultrafiltration. All of them gave comparable results for the gyrase inhibitors nalidixic acid, ofloxacin, and gatifloxacin with regard to the extent of protein binding. The relaxation measurements revealed the quinolone moiety to be the main interaction partner with the protein whereas the piperazine moieties are not involved in the binding process.